In the Chemical Processing Industries (CPI) process control is an important consideration. Issues associated with process control are often complex and non-linear and require human judgment and experience.
One example of a chemical process with control issues occurs during waste separation processes in the petroleum industry. For example, in the production of crude oil, contaminants in the solid phase and contaminants in the liquid phase may be present in a mixture containing the oil. Excessive levels of contaminants yield a final product that is non-usable. In addition, contaminated crude oil can be difficult to dispose of in an environmentally safe manner.
One separation system for oil mixtures includes a three stage centrifuge which mechanically separates the contaminants from the oil. U.S. Pat. No. 5,156,751 to Miller discloses this type of system. The control of such a system is difficult because there are several variables that affect the separation process and the purity of the final product. These variables are difficult to model and incorporate into a control system for the centrifuge.
For example, the oil mixture enters the centrifuge as a meta-stable emulsion containing two liquid phases (oil and water) and a solid phase (solids). The physical properties of the mixture required for modeling the control system, are variable and not well understood. In addition, the mechanics of the centrifuge introduce variables that are also difficult to characterize and quantify. The centrifuge includes a tapered bowl and an internal conveyor auger rotating at different rotational speeds. The solids and the oil separate from the water at different rates depending on the rotational speeds of the bowl and the auger. Further, the feed rate and the temperature of the oil mixture, the size of the solids, and the type of the oil, also affect the separation process. In addition, during the separation process the oil and the water can interact in an unpredictable manner. Even a simple model of this system does not represent it well enough to be used for control purposes.
In view of the multitude of variables, in the past a skilled operator with broad experience and intuitive knowledge is required to successfully operate the separation system. However, skilled operators are difficult to train, and expensive to pay. It would be advantageous to utilize the experience and intuitive knowledge of a skilled operator to formulate an automated control system for the separation system.
The present invention recognizes that fuzzy logic techniques can be utilized to construct an automated control system that simulates the experience and judgment of a skilled operator. Rather than modeling the system, the fuzzy logic models the skilled operator.